Asthma is a complex disease involving the concerted actions of multiple inflammatory and immune cells, spasmogens, inflammatory mediators inflammatory, cytokines and growth factors. In recent practice there have been four major classes of compounds used in the treatment of asthma, namely bronchodilators (e.g., xcex2-adrenoceptor agonists), anti-inflammatory agents (e.g., corticosteroids), prophylactic anti-allergic agents (e.g., cromolyn sodium) and xanthines (e.g., theophylline) which appear to possess both bronchodilating and anti-inflammatory activity.
Theophylline has been a preferred drug of first choice in the treatment of asthma. Although it has been touted for its direct bronchodilatory action, theophylline""s therapeutic value is now believed to also stem from anti-inflammatory activity. Its mechanism of action remains unclear. However, it is believed that several of its cellular activities are important in its activity as an anti-asthmatic, including cyclic nucleotide phosphodiesterase inhibition, adenosine receptor antagonism, stimulation of catecholamine release, and its ability to increase the number and activity of suppressor T-lymphocytes. While all of these may actually contribute to its activity, only PDE inhibition may account for both the anti-inflammatory and bronchodilatory components. However, theophylline is known to have a narrow therapeutic index and a wide range of untoward side effects which are considered problematic.
Of the activities mentioned above, theophylline""s activity in inhibiting cyclic nucleotide phosphodiesterase has received considerable attention recently. Cyclic nucleotide phosphodiesterases (PDEs) have received considerable attention as molecular targets for anti-asthmatic agents. Cyclic 3xe2x80x2,5xe2x80x2-adenosine monophosphate (cAMP) and cyclic 3xe2x80x2,5xe2x80x2-guanosine monophosphate (cGMP) are known second messengers that mediate the functional responses of cells to a multitude of hormones, neurotransmitters and autocoids. At least two therapeutically important effects could result from phosphodiesterase inhibition, and the consequent rise in intracellular adenosine 3xe2x80x2,5xe2x80x2-monophosphate (cAMP) or guanosine 3xe2x80x2,5xe2x80x2-monophosphate (cGMP) in key cells in the pathophysiology of asthma. These are smooth muscle relaxation (resulting in bronchodilation) and anti-inflammatory activity.
It has become known that there are multiple, distinct PDE isoenzymes which differ in their cellular distribution. A variety of inhibitors possessing a marked degree of selectivity for one isoenzyme or the other have been synthesized.
The structure-activity relationships (SAR) of isozyme-selective inhibitors has been discussed in detail, e.g., in the article of Theodore J. Torplhy, et al., xe2x80x9cNovel Phosphodiesterases Inhibitors For The Therapy Of Asthmaxe2x80x9d, Drug News and Prospectives, 6(4) May 1993, pages 203-214. The PDE enzymes can be grouped into five families according to their specificity toward hydrolysis of cAMP or cGMP, their sensitivity to regulation by calcium, calmodulin or cGMP, and their selective inhibition by various compounds. PDE I is stimulated by Ca2+/calmodulin. PDE II is cGMP-stimulated, and is found in the heart and adrenals. PDE III is cGMP-inhibited, and inhibition of this enzyme creates positive inotropic activity. PDE IV is cAMP specific, and its inhibition causes airway relaxation, antiinflammatory and antidepressant activity. PDE V appears to be important in regulating cGMP content in vascular smooth muscle, and therefore PDE V inhibitors may have cardiovascular activity.
While there are compounds derived from numerous structure activity relationship studies which provide PDE III inhibition, the number of structural classes of PDE IV inhibitors is relatively limited. Analogues of rolipram, which has the following structural formula: 
and of RO-20-1724, which has the following structural formula: 
have been studied.
U.S. Pat. No. 4,308,278 discloses compounds of the formula (C) 
Wherein R1 is (C3-C6) cycloalkyl or benzyl; each of R2 and R3 is hydrogen or (C1-C4) alkyl; R4 is R2 or alkoxycarbonyl; and R5 is hydrogen or alkoxycarbonyl.
Compounds of Formula (D)) are disclosed in U.S. Pat. No. 3,636,039. These compounds are benzylimidazolidinones which act as hypertensive agents. 
Substituents R1-R4 in Formula D represent a variety of groups, including hydrogen and lower alkyl.
PCT publication WO 87/06576 discloses antidepressants of Formula E: 
wherein R1 is a polycycloalkyl group having from 7 to 11 carbon atoms; R2 is methyl or ethyl; X is O or NH; and Y comprises of a mono-or bycyclic heterocyclic group with optional substituents.
Rolipram, which was initially studied because of its activity as an anti-depressant, has been shown to selectively inhibit the PDE IV enzyme and this compound has since become a standard agent in the classification of PDE enzyme subtypes. There appears to be considerable therapeutic potential for PDE IV inhibitors. Early work focused on depression as a CNS therapeutic endpoint and on inflammation, and has subsequently been extended to include related diseases such as dementia and asthma. In-vitro, rolipram, RO20-1724 and other PDE IV inhibitors have been shown to inhibit (1) mediator synthesis/release in mast cells, basophils, monocytes and eosinophils; (2) respiratory burst, chemotaxis and degranulation in neutrophils and eosinophfils; and (3) mitogen-dependent growth and differentiation in lymphocytes (The PDE IV Family Of Calcium-Phosphodiesterases Enymes, John A. Lowe, III, et al., Drugs of the Future 1992, 17(9):799-807).
PDE IV is present in all the major inflammatory cells in asthma including eosinophils, neutrophils, T-lymphocytes, macrophages and endothelial cells. Its inhibition causes down regulation of inflammatory cell activation and relaxes smooth muscle cells in the trachea and bronchus. On the other hand, inhibition of PDE III, which is present in myocardium, causes an increase in both the force and rate of cardiac contractility. These are undesirable side effects for an anti-inflammatory agent. Theophylline, a non-selective PDE inhibitor, inhibits both PDE III and PDE IV, resulting in both desirable anti-asthmatic effects and undesirable cardiovascular stimulation. With this well-known distinction between PDE isozymes, the opportunity for concomitant anti-inflammation and bronchodilation without many of the side effects associated with theophylline therapy is apparent. The increased incidence of morbidity and mortality due to asthma in many Western countries over the last decade has focused the clinical emphasis on the inflammatory nature of this disease and the benefit of inhaled steroids. Development of an agent that possesses both bronchodilatory and antiinflammatory properties would be most advantageous.
It appears that selective PDE IV inhibitors should be more effective with fewer side effects than theophylline. Clinical support has been shown for this hypothesis. Furthermore, it would be desirable to provide PDE IV inhibitors which are more potent and selective than theophylline and therefore have a lower IC50 so as to reduce the amount of the agent required to effect PDE IV inhibition.
In recent years, several different compounds have been suggested as possible therapeutic compositions which achieve the desired PDE IV inhibition without the side effects alluded to above. However, these efforts have been chiefly directed to developing non-specific derivatives of particular classes of compounds, i.e. rolipram analogs, benzoxazoles, adenines, thioxanthines, etc. These efforts, however, have resulted in a myriad of compounds having a wide range of PDE IV IC50""s. Often, the general formulas disclosed yield several compounds which have poor levels of PDE IV inhibition and/or lack sufficient specificity. Consequently, these efforts often provide no assurance that any particular derivative within the formula will have the desired combination of high PDE IV inhibition and selectivity.
It is accordingly a primary object of the present invention to provide new compounds which have a superior PDE IV inhibitory effect as compared to theophylline or other known compounds.
It is another object of the present invention to provide new compounds which act as effective PDE IV inhibitors with lower PDE III inhibition.
It is a further object of the present invention to provide new compounds which exhibit surprisingly greater selectivity with regard to their PDE IV inhibitory effects.
It is another object of the present invention to provide a method of treating a patient requiring PDE IV inhibition.
It is another object of the present invention to provide new compounds for treating disease states associated with abnormally high physiological levels of inflammatory cytokines, including tumor necrosis factor.
It is another object of the present invention to provide a method of synthesizing the new compounds of this invention.
With the above and other objects in view, one aspect of the invention includes PDE IV inhibitor compounds containing a fused 6,5-membered ring system with a substitution pattern that yields compounds having a high degree of selective PDE IV inhibition and an IC50 below that of theophylline. The present invention includes compounds of Formula I: 
wherein:
rings xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d can be saturated, unsaturated or partially unsaturated;
X1 is selected from CH, Cxe2x80x94Cl, or N;
X2 is selected from CR12 or N;
X3 is selected from CH or N;
X4 is selected from CH or N;, wherein at least one of X to X4 is not N;
P1, P2 are independently selected from C, O or N; CH, O, N or NH;
M is selected from CH, C, or N;
Q is C1-C3 alkyl or xe2x80x94CHxe2x95x90CHxe2x80x94;
R6 is selected from xe2x80x94C(R9)3, xe2x80x94CH(R9)2, or xe2x80x94C3-C8-cycloalkyl;
R7 is selected from xe2x80x94SH, OH or xe2x80x94CHO;13 
R8 is selected from xe2x80x94C(R9)3, xe2x80x94CH(R9)2, xe2x80x94C3-C8-cycloalkyl, or xe2x80x94C2H4xe2x80x94C6-cycloalkyl;
R10 is selected from xe2x80x94C1-C3-pyridyl, xe2x80x94C3H6OH, xe2x80x94Cxe2x89xa1Cxe2x80x94, Br, xe2x80x94Cxe2x89xa1Cxe2x80x94CH2OH, isopropyl, hydrogen, 
R11 is selected from H, xe2x80x94OH, xe2x80x94Oxe2x80x94C3-C8-cycloalkyl, xe2x80x94C3-alkyl, xe2x80x94Z-pyridyl, xe2x80x94Z-trienyl, and xe2x80x94Zxe2x80x94CH2OH;
R12 is selected from xe2x80x94SH, H, halogen or lower alkyl;
R9 is lower alkyl, and
Z is selected from ethyl, and xe2x80x94Cxe2x95x90Cxe2x80x94H.
Other aspects of the invention include methods of synthesizing the compounds described above as well as pharmaceutical compositions containing the same. Still further aspects of the invention include methods of treating PDE IV-susceptible conditions in mammals by administering an effective amount of the compositions described herein.
The compounds of the present invention are effective in the selective mediation or inhibition of PDE IV in mammals. These compounds possess both bronchodilatory and antiinflammatory properties which are substantially without the undesirable cardiovascular stimulation which is caused by PDE III inhibition. The compounds of the present invention have a PDE IV inhibitory effect which is greater than rolipram or theophylline.
The PDE IV inhibitor compounds of the present invention are based on a fused 6,5-membered ring system compounds having a high degree of selective PDE IV inhibition and an IC50 below that of rolipram. This selective blocking has been unexpectedly achieved by compounds of Formula I: 
wherein:
rings xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d can be saturated, unsaturated or partially unsaturated;
X1 is selected from CH, Cxe2x80x94Cl, or N;
X2 is selected from CR12 or N;
X3 is selected from CH or N;
X4 is selected from C or N;
P1, P2 are independently Selected from C, O or N;
M is selected from CH, C, or N;
Q is C1-C3 alkyl or xe2x80x94CHxe2x95x90CHxe2x80x94;
R6 is selected from xe2x80x94C(R9)3, xe2x80x94CH(R9)2, or xe2x80x94C3-C8 cycloalkyl;
R7 is selected from xe2x80x94SH, or xe2x80x94CHO;
R8 is selected from xe2x80x94C(R9)3, xe2x80x94CH(R9)2, xe2x80x94C3-C8-cycloalkyl, or xe2x80x94CH2xe2x80x94C4-C6-cycloalkyl;
R10 is selected from C1-C3-pyridyl, C3H6OH, xe2x80x94Cxe2x89xa1Cxe2x80x94, Br, xe2x80x94Clxe2x89xa1C3xe2x80x94CH2OH, isopropyl, hydrogen, 
R11 is selected from H, xe2x80x94OH, xe2x80x94Oxe2x80x94C3-C8-cycloalkyl, xe2x80x94SH, xe2x80x94Z-pyridyl, xe2x80x94Z-trienyl, and xe2x80x94Zxe2x80x94CH2OH;
R12 is selected from xe2x80x94SH, H, halogen or lower alkyl;
R9 is lower alkyl; and
Z is selected from ethyl, and xe2x80x94Cxe2x89xa1Cxe2x80x94.
Preferred compounds have a structure of Formula II, 
wherein
R6 is selected from xe2x80x94C(R9)3, xe2x80x94CH(R9)2, and C3-C8-cycloalkyl;
R7 is selected from xe2x80x94OH, xe2x80x94SH, xe2x80x94Oxe2x80x94COxe2x80x94CH3, and xe2x80x94CHO;
R8 is selected from xe2x80x94C(R9)3, xe2x80x94CH(R9)2, and xe2x80x94CH2xe2x80x94C4-C6-cycloalkyl;
Q is selected from xe2x80x94C1-C2-alkyl and xe2x80x94CHxe2x95x90CHxe2x80x94;
R10 is selected from C1-C3-pyridyl, C3H6OH, xe2x80x94Cxe2x89xa1Cxe2x80x94, Br, xe2x80x94Cxe2x89xa1Cxe2x80x94C3H2OH, isopropyl, hydrogen, 
R11 is selected from H, xe2x80x94OH, xe2x80x94Oxe2x80x94C3-C8-cycloalkyl, xe2x80x94SH, xe2x80x94Z-pyridyl, xe2x80x94Z-trienyl, and xe2x80x94Zxe2x80x94CH2OH;
X1 is selected from CH and Cxe2x80x94Cl;
R9 is lower alkyl; and
Z is selected from ethyl and xe2x80x94Cxe2x89xa1Cxe2x80x94.
Further preferred are compounds of Formula II wherein
R6 is selected from xe2x80x94C(CH3)3, and xe2x80x94CH(CH3)2;
R7 is selected from xe2x80x94OH and xe2x80x94Oxe2x80x94COxe2x80x94CH3;
R8 is selected from xe2x80x94C(CH3)3, and xe2x80x94CH(CH3)2;
Q is selected from xe2x80x94C1-C2-alkyl and xe2x80x94CHxe2x95x90CHxe2x80x94;
R10 is selected from C1-C3-pyridyl, C3H6OH, xe2x80x94Cxe2x89xa1Cxe2x80x94, Br, xe2x80x94Cxe2x89xa1Cxe2x80x94C3H2OH, isopropyl, hydrogen, 
Particularly preferred compounds of the present invention include:
1. 5-chloro-2-(3,5-di-t-butyl-4-hydroxy-benzyl)-7-(2-(2-pyridyl)-ethynyl)-benzoxazole;
2. 2-((3,5-Di-t-butyl-4-hydroxy)benzyl-7-(2-(2-pyridyl)-ethynyl)-benzoxazole;
3. 5-chloro-2-(3,5-di-t-butyl-4-hydroxy-benzyl)-7-(2-(2-thiazolyl)-ethynyl)-benzoxazole; and
4. 3-(5-chloro-2-(4-hydroxy3,5bis((1,1dimethyl)ethyl)benzyl)benzoxazol-7-yl)prop-2-yn-1-ol.
The present invention includes pharmaceutical compositions of compounds of Formula I and Formula II; methods of effecting selective PDE IV inhibition in mammals requiring the same, which comprises administering an effective amount of a compound of Formula I and Formula II; methods of treating a mammal suffering from a disease state selected from a group consisting of asthma, allergies, inflammation, dementia, atopic diseases, rhinitis, and disease states associated with abnormally high physiological levels of cytokine, comprising administering an effective amount of a compound of Formula I and Formula II.
The present invention also includes pharmaceutically acceptable salts and prodrugs of all the compounds of the present invention. Pharmaceutically acceptable salts include those in which the main compound functions as a base, e.g., hydrochloride, as well as those for which the main compound functions as an acid, e.g., choline salts.
The compositions of the present invention can be prepared using standard organic methods. See, for example, commonly assigned PCT/GB94/01334 having PCT International Publication No. WO 95/00516, the contents of which are hereby incorporated by reference. Details concerning preparing some of the preferred compounds are provided in the Examples section below.
In view of the high degree of selective PDE IV inhibition, the compounds of the present invention can be administered to anyone requiring PDE IV inhibition. Administration may be accomplished orally, topically, by suppository, inhalation or insufflation, or parenterally.
The present invention also encompasses all pharmaceutically acceptable salts of the foregoing compounds. One skilled in the art will recognize that acid addition salts of the claimed compounds may be prepared by reaction of the compounds with the appropriate acid via a variety of known methods. Alternatively, alkali and alkaline earth metal salts are prepared by reaction of the compounds of the invention with the appropriate base via a variety of known methods. For example, the sodium salt of the compounds of the invention can be prepared via reacting the compound with sodium hydride.
Various oral dosage forms can be used, including such solid forms as tablets, gelcaps, capsules, caplets, granules, lozenges and bulk powders and liquid forms such as emulsions, solution and suspensions. The compounds of the present invention can be administered alone or can be combined with various pharmaceutically acceptable carriers and excipients known to those skilled in the art, including but not limited to diluents, suspending agents, solubilizers, binders, disintegrants, preservatives, coloring agents, lubricants and the like.
When the compounds of the present invention are incorporated into oral tablets, such tablets can be compressed, tablet triturates, enteric-coated, sugar-coated, filmcoated, multiply compressed or multiply layered. Liquid oral dosage forms include aqueous and nonaqueous solutions, emulsions, suspensions, and solutions and/or suspensions reconstituted from non-effervescent granules, containing suitable solvents, preservatives, emulsifying agents, suspending agents, diluents, sweeteners, coloring agents, and flavorings agents. When the compounds of the present invention are to be injected parenterally, they may be, e.g., in the form of an isotonic sterile solution. Alternatively, when the compounds of the present invention are to be inhaled, they may be formulated into a dry aerosol or may be formulated into an aqueous or partially aqueous solution.
In addition, when the compounds of the present invention are incorporated into oral dosage forms, it is contemplated that such dosage forms may provide an immediate release of the compound in the gastrointestinal tract, or alternatively may provide a controlled and/or sustained release through the gastrointestinal tract. A wide variety of controlled and/or sustained release formulations are well known to those skilled in the art, and are contemplated for use in connection with the formulations of the present invention. The controlled and/or sustained release may be provided by, e.g., a coating on the oral dosage form or by incorporating the compound(s) of the invention into a controlled and/or sustained release matrix.
Specific examples of pharmaceutically acceptable carriers and excipients that may be used for formulate oral dosage forms, are described in the Handbook of Pharmaceutical Excipients, American Pharmaceutical Association (1986), incorporated by reference herein. Techniques and compositions for making solid oral dosage forms are described in Pharmaceutical Dosage Forms: Tablets (Lieberman, Lachman and Schwartz, editors) 2nd edition, published by Marcel Dekker, Inc., incorporated by reference herein. Techniques and compositions for making tablets (compressed and molded), capsules (hard and soft gelatin) and pills are also described in Remington""s Pharmaceutical Sciences (Arthur Osol, editor), 1553-1593 (1980), incorporated herein by reference. Techniques and composition for making liquid oral dosage forms are described in Pharmaceutical Dosage Forms: Disperse Systems, (Lieberman, Rieger and Banker, editors) published by Marcel Dekker, Inc., incorporated herein by reference.
When the compounds of the present invention are incorporated for parenteral administration by injection (e.g., continuous infusion or bolus injection), the formulation for parenteral administration may be in the form of suspensions, solutions, emulsions in oily or aqueous vehicles, and such formulations may further comprise pharmaceutically necessary additives such as stabilizing agents, suspending agents, dispersing agents, and the like. The compounds of the invention may also be in the form of a powder for reconstitution as an injectable formulation.
The dose of the compounds of the present invention is dependent upon the affliction to be treated, the severity of the symptoms, the route of administration, the frequency of the dosage interval, the presence of any deleterious side-effects, and the particular compound utilized, among other things.
The present invention is further related to a method for the treatment of allergic and inflammatory disease which comprises administering to a mammal in need thereof an effective amount of the compounds of the present invention.
The present invention is also related to a method for the mediation or inhibition of the enzymatic or catalytic activity of PDE IV activity in mammals, particularly humans, which comprises administering an effective amount of the above-described compounds of the invention to a mammal in need of PDE IV inhibition.
The compounds of the present invention may find use in the treatment of other disease states in humans and other mammals, such as in the treatment of disease states associated with a physiologically detrimental excess of tumor necrosis factor (TNF). TNF activates monocytes, macrophages and T-tymphocytes. This activation has been implicated in the progression of Human Immunodeficiency Virus (HIV) infection and other disease states related to the production of TNF and other cytokines modulated by TNF.